Typical communication networks such as wide area wireless networks have a hierarchical infrastructure. For example, in wide area wireless networks, mobile devices communicate with base stations (or BTSs—base transceiver stations) deployed over a large area and multiple base stations are controlled by centralized nodes (such as BSCs—base station controllers or a RNCs—radio network controllers). These controllers may or may not be connected and/or controlled further by a next higher-level node, such as a mobile switching center (MSC).
In the converged voice/data network architecture, the next higher level node above the BSCs or RNCs may be an IP Multimedia Subsystem (IMS) instead of a traditional MSC. Or, the IP IMS may be a node at a higher level than the MSC and connected to multiple MSCs.
The nodes in this hierarchical structure have various hardware and other resource limitations. Consequently, these nodes perform admission and overload control functions to ensure that a high load does not create unstable operating conditions and that there are enough resources to support end-to-end connectivity once a call is admitted to the system. When an extraordinary access load occurs, for example, such as due to an emergency situation, a significant number of call access attempts may be denied/blocked.
The blocking may occur at different levels of infrastructure hierarchy. Once the blocking has occurred, the call request is dropped at the node at which the blocking has occurred. The call originator is forced to retry access connection after some time.
In such a situation, the call target may never be notified that a call was intended for them.